Sheet glass drawing

ABSTRACT

Method and apparatus for improving the quality of a drawn flat glass ribbon by providing for a flow of gas currents between the annealing lehr and the drawing chamber along paths which are in addition to the usual slot that the glass ribbon passes through when moving from the drawing chamber to the annealing lehr. In certain embodiments gas from the lower portion of the drawing chamber moves into the annealing lehr through special means which are provided.

United States Patent 1191 Lambert et all SHEET GLASS DRAWING Inventors:Michael Lambert, Brussels; Hubert Neuzy, Montignies/s/Sambre; ClaudeBrichard, Moustier/s/Sambre, all of Belgium Assignee: Glaverbel S.A.,

Watermael-Boitsfort, Belgium Filed: July 14, 1972 App]. No.: 271,759

Foreign Application Priority Data Apr. 14, 1971 Luxembourg 63534 July 6,1972 Great Britain 31766/72 us. c1. 65/95, 65/194, 65/204 Int. Cl 003115/04 Field of Search 65/95, 96, 193, 194, 196,

1111' 3,801,296 14 1 Apr. 2,' 1974 References Cited UNITED STATESPATENTS 2,475,773 7/1949 Batchell 65/95 X 2,726,486 12/1955 Brichard65/95 X 2,695,052 1 H1954 Brichard 155/84 Primary Examiner-Arthur D.Kellogg 57 ABSTRACT Method and apparatus for improving the quality of aI drawn flat glass ribbon by providing for a flow of gas currentsbetween the annealing lehr and the drawing chamber along paths which arein addition to the usual slot that the glass ribbon passes through whenmoving from the drawing chamber to the annealing lehr. In certainembodiments gas from the lower portion of the drawing chamber moves intothe annealing lehr through special means which are provided.

- 18 Claims, 5 Drawing Figures 1 SHEET GLASS'DRAWING BACKGROUND OF THEINVENTION- The present invention relates to a process of manufacturingsheet glass by'supplying molten glass to a drawing zone and drawingglass from that zone as a continuous ribbon through a drawing chamberand into a contiguous annealing lehr, tunnel or shaft via a slot throughwhich gas convection currents also flow from the drawing chamber intothe shaft and vice versa. The invention also relates to apparatus foruse in manufac turing sheet glass by this process.

There are various known processes for manufacturing sheet glass bydrawing a ribbon of molten glass from a drawing zone to which moltenglass is supplied. In some of these processes the ribbon is drawn fromthe surface of a quantity of molten glass flowing to the drawing zone.An example of such a process is the classical Pittsburgh process inwhich the molten glass which flows into the ribbon is derived from theupper levels of a bath of molten glass. Another example of sucha'process is the classical Libbey-Owens or Colburn process in whichmolten glass flows into the ribbon from the full depth of a relativelyshallow bath.

Surface drawing processes are not confined to the classical ones whichhave been specifically mentioned. For example, it is known to draw theribbon from a sup ply of molten glasswhich is fed to the drawingzonewhile floating on a bath or layer of molten material, e.g., a moltenmetal, of higher specific gravity, acting as a lubricant between themolten glass and the sole of a refractory kiln inwhich the moltenmaterials are held. As another example of a special type of surfacedrawing process, the ribbon of glass, instead of being drawn via ameniscus formed at a free fluid surface of the supply ofmolten glass,may be drawn from a meniscus which is cooled to prevent flow of moltenglass beyond the locations of the meniscus as e.g., is described inUnited Kingdom Pat. No. 988,128. Although they are not so important forthe purpose of introducing the present invention, mention is also madeof processes in which the ribbon of glass is extruded from beneath thesurface of the supply of molten glass, e.g., as in the classicalFourcault process.

In all of the known processes of drawing a ribbon of glass from a supplyof molten glass, the ribbon is drawn from the drawing zone through adrawing chamber in which the ribbon becomes dimensionally set and theribbon passes from the drawing chamber via an exit slot into a shaft inwhich the ribbon progressively cools preparatory to being cut intosections.

in all of such known glass drawing processes, the glass ribbonis exposedto the influence of environmental gas currents which exert, on theribbons, a cooling action which is irregular in both time and space.These currents are due to various causes. Due to the interconnection ofthe drawing chamber and the annealing shaft, the shaft has a chimneyeffect, causing a system of natural draft currents to propagate throughthe drawing chamber and the annealing shaft; Hot gas currents flowupwardly along the central region of the ribbon from the intensely hotdrawing zone, through the drawing chamber and into the annealing shaftvia the aforesaid slot, and cooler currents of gases nearer the sidewalls of the apparatus flow back through such slot into the drawingchamber from the annealing shaft.

2 The chimney effect is particularly marked when the annealing shaft isvertical.

The rising currents of hot gas caused by the aforesaid chimney effectincrease in temperature and velocity during their movement through-thedrawing chamber and give rise to turbulence in the upper part of thechamber. There is an interaction between these turbulent currents andthe natural draft currents which flow from the drawing chamber into theannealing shaft and vice versa. This interaction gives-rise to'a complexsystem of currents which plays a part in creating adverse heatdistribution across the ribbon.

Some of the cooler gas flowing back into the drawing chamber from theannealing shaft tends to flow down within the drawing chamber along thewalls thereof and then, as it becomes heated, to flow inwardly alonggenerally upwardly inclined paths to join the main upward convectioncurrent of gas along the central longitudinal portion of the ribbonpath. In the course of such flow some of this cooler gas sweeps acrossthe marginal zones of the ribbon path and verse conditions.

SUMMARY OF'THE INVENTION The object of the present invention isto-provide a form of corrective measure which influences the conditionsto which the faces of the drawn glass ribbon are exposed, so as to makepossible, an improvement in the realizable quality of sheet glass. 7 f Ii According to the present invention,there is provided a process ofmanufacturing'sheet glass by-supplying molten glass to a drawing zoneand'dr awing glass from slot through which gas convection currents alsoflow from the drawing chamber into the shaft and vice versa.

Gases are also caused to flow between the interior of i the drawingchamber and the interior of the annealing shaft via at least one pathadditional to that which is provided by the slot.

The provision of at least one additional flow path reduces the volumerate of flow of gas between the drawing chamber and theannealingshaftvia the aforesaid slot in which the convection currents ofgases are necessarily contrainedto flow in closefcontactwith thefaces-of the glass ribbon. In consequence, the pattern of gas currentsin the upper part of the drawing chamber is modified. The modification.is such asto produce more favorable heat distribution in the environmentof the ribbon at this region as is indicated by the fact that sheetglass drawn by a process according to the invention has been found to beless impaired by the effects of turbulent, thermally heterogeneouscurrents than sheet glass drawn in a process inwhich no such additionalgas flow path was provided but which was otherwise identical. I

It' is emphasized that the invention aims to obviate surface defectswhich are caused by adverse environmental conditions in the upper partof the drawing chamber. It is assumed in the present specification thatother measures may also be taken when necessary to keep the drawn sheetglass as free as possible from defects produced by other types ofenvironmental currents. By way of example, gas displacing forces may beexerted in the lower part of the drawing chamber to cause gases in theenvironment of the ribbonto .undergo to-and-fro movement across thefaces of the ribthis also gives rise to adbon in order to avoid orreduce the adverse thermal gradients or inequalities which areresponsible for the formation ofwaves in the faces of the drawn glass.As certain of the measures for countering the formation of the moreserious surface defects areknown per se they will not be referred to inthe following description pertaining to the performance of the presentinvention.

* Preferably, there is at least one such additional path along whichgases flow from the drawing chamber into the annealing shaft. it has.been found that the attainment of the required results, namely, animprovement in he heat distribution in the vicinity of the top of thedrawing chamber is greatly assisted by reducing the mass and velocity ofgases flowing upwardly through the aforesaid. slot under the naturalshaft forces. The effect of this reduction in the kinetic energy of thegases passingthrough' the ribbon slot is to reduce the uncontrolledturbulent currents flowing against the surface of the ribbon.

. In certain embodiments of the invention, the flow of gases which takesplace between the interior of the drawing chamber and the interior ofthe annealing shaft, via such additional path or paths, is wholly orpredominantly a flow from the drawing chamber to the annealing shaft.

his very suitable. for the gases ascending'via at leas onesuch'additiona l path tobe introduced into the annealing shaft at alevel a short distance above the ribbon'slot, e-.g., at a level betweensuch slot and the'lowest pair of drawing rollers in the shaft.

Advantageously, there is at least one such additional flow pathvia'which gases flow into the annealing shaft from the upper part of thedrawing chamber. If the additional flow path or paths for conductinggases into the annealing shaft is or are traversed by gases which havealready flowed upwardly into the upper part of the drawing chamber theprocess can be performed without substantially modifying the normaltemperature gradient along the ribbon path if so desired.

in certain processes according to the invention, there is at least 'onesuch additional flow path for gases through the top of the drawingchamber, i.e., in. the wall or-walls defining the aforesaid ribbon slot.It is particularly easyito provide such an additional flow path bymaking such wall orwalls of appropriate form or by modifying standardwall components, e.g., the conventional catch pans at the bottom of theannealing shaft, to provide such an additional path or paths throughsuch wall components.

The invention also includes processes in which there is at least onesuch'additional flow path via which gases descend into the drawingchamber from the annealing shaft. The descending relatively coolcurrents of gas flow mainly'along the outer regions of the ribbon path,i.e., in general terms, in regions opposite the outer third portions ofthe projected width of the ribbon. It appears that in many cases thethennally heterogeneous turbulent currents contributing to the adverseheat distribution in the upper part of the drawing chamber are due to anappreciable extent or even entirely, to the behavior of the descendingcoolercurrents of gases as they pass through the ribbon slot and thenexpand in the upper part of the drawing chamber. By providing analternative flow path or alternative flow paths for such descendinggases so that a proportion of the descending gases bypasses the ribbonslot, the environmental con- 4. ditions in the upper part of the drawingchamber are improved. i I

In the most preferred embodiments of the invention, gases flow from theinterior of the drawing chamber into the annealing shaft and also fromthe annealing shaft into the drawing chamber, via at least one suchadditional path. In such processes there is a reduced flow of gasesthrough the ribbon slot in both the ascending and the descendingconvectioncurrents and the favorable effect on the environmentalconditions in the top portion of the drawing chamber and at thelocations of the ribbon slot is particularly marked. in general terms,the ascending convection currents of gas are mainly within the centralthird portion of the intended or projected width of the ribbon so that,for causing gases which would normally pass through the ribbon slot withthat current to by-pass the slot, it is necessary to provide at leastone such additional flow path which 7 is open to the drawing chamber atleast within that central portion. The descending cooler convection cur'rents of gas on the other hand are mainly within the outer thirdportions of the projected width of the ribbon so that in order to reducethe flow of descending cooler gas through the ribbon slot it isnecessary to provide at least one such additional flow path which isopen to the annealing shaft at least within one of such outer portions.The most pronounced beneficial effect on-the environmental conditions inthe vicinity of the top of the drawing chamber are achieved byembodiments of the present invention in which gases are caused to flowfrom the drawing chamber into the annealing shaft via at least one suchadditional flow path located within the central third of the projectedwidth of the glass ribbon and gases are caused simultaneously to flowfrom the annealing shaft into the drawing chamber via at least one suchadditional path located in each of the outer thirds of the projectedwidth of the ribbon. An ascending and a descending flow of gases,bypassing the ribbon slot; may. take place via one and the sameadditional flow path if there is a path in the form of a slot whichextends over the full projected width of the ribbon path or the greaterpart of such width.

The invention includes processes in which a flow of gases via at leastone additional flow path takes place as a result 'of natural'convecti'oncurrents. By making use of the inherent energy of the convectioncurrents the need for gas displacing devices to promote or cause flow ofgases along the additional path or paths is obviated.

Advantages are to be gained by causing a flow of gases along anadditional flow path or paths confined to one side of the ribbon This isbecause in certain processes it may be found that inthe normal way oneface of theglass ribbon is less prone'to be marred than the other face,this being a result of a difference'between the environmental conditionsat the opposed sides of the glass ribbon. Nevertheless in preferredembodiments of the invention,,gases are cauesed to flow between theinterior of the drawing chamber and the interior of the annealing shaftvia at least one additional flow path on each side of the glass ribbon.

in certain embodiments of processes according to the invention a flow ofgases from the annealing shaft into the drawing chamber takes placealong one or more additional flow paths formed in such a way that gasesdescending via such additional path or paths are dispersed at or nearthe top of the drawing chamber. The descending gases may for example bedispersed. in the sense that they are spatially distributed over alarger area, or dispersed in the sense that their energy is partlyabsorbed. By dispersing such gases they are rendered less liabletocontribute to the creation of thermally heterogeneous turbulentcurrents acting against the surface of the glass ribbon in the upperpart of the drawing chamber and the purpose in view is accordinglyfurther promoted.

Advantageously, descending and ascending gases are caused to flow viaadditional flow paths formed so that gases moving in one direction aredispersed into gases moving in the other direction. As a result, thereis a mixing of opposed gas currents and this has been found to bebeneficial for promoting a favorable heat distribution.

According to other embodiments of the invention, a flow of gases fromthe annealing shaft into the drawing chamber takes place along one ormore additional flow paths which is or are formed so as to disperse suchdescending gases away from the path of the ribbon. This is the mosteffective way of preventing such gases from directly acting on the glassribbon in the upper part of the drawing chamber.

In certain special embodiments of the invention, gases are caused toflow intothe annealing shaft, via at least one additional path, from aregion in the lower part of the drawing chamber. By causing such a flowof gases there is brought about not only an improvement in the thermaland dynamic flow conditions in the region of transition from the'drawingchamber to the annealing shaft, as a result of the reduced upward flowof gases through the ribbon slot, but also an improvement in theenvironmental condition of the ribbon in the lower part of the drawingchamber such as to reduce the tendency for the drawn sheet glass to beimpaired by thermally heterogeneous convection currents. The withdrawalof gases from a region in the lower part of the drawing chamber andtheir introduction into the annealing shaft can, in certaincircumstances, be relied upon for avoiding defects in the sheet glass. V

In certain processes according to the invention wherein the glass ribbonis drawn past at least one cooler in the lower part of the drawingchamber, a flow of gasesalong at least one additional flow path takesplace from at least one region in the vicinity ofa cooler. Thewithdrawal of gases which have been cooled by a main cooler isparticularly recommended for the purposes of creating environmentalconditions which favor the production of sheet glass with facessubstantially free from defects.

It has been found that in some cases the invention afthe upper part ofthe drawing chamber. There is occasionally the tendency for the adversethermal conditions in the upper part of the drawing chamber which tendto cause defects in the faces of the sheet glass to be accentuated bythe action of such secondary cooler or coolers. By means of theinvention this influence of secondary coolers can be countered. Inaddition it has been found that in such cases the by-pass flow of gasesin accordance with the invention is responsible for modifying theeffects of secondary coolers on the gaseous environment in the upperpart of the drawing chamber in such a way as to improve still more thequality of the faces of the sheet glass.

Particular importance is attached to processes according to theinvention in which the annealing shaft is a vertical shaft surmoun tingthe drawing chamber, as e.g., in a classical Pittsburgh-type glassdrawing process.

The invention can be applied successfully in a wide variety of glassdrawing processes, for example, in a process in which molten glass flowsinto the ribbon from the full depth of a quantity of molten glass in achannel into which molten glass is continuously fed, in a process inwhich molten glass flows into the ribbon from the upper levels of a massof molten glass in a channel into which molten glass is continuouslyfed, and in a process in which the ribbon is drawn from molten glassfloating on a mass of material of higher specific gravity.

The invention includes apparatus for use in manufacturing sheet glass,including a drawing chamber, a contiguous annealing shaft whichcommunicates with such drawing chamber via a slot and means for drawinga continuous ribbon of glass from a supply of molten glass at a drawingzone so that the ribbon passes through such drawing chamberand into theannealing shaft via the said slot. Convection currents of gases alsoflow through. such slot from the drawing chamber into the annealingshaft and vice versa. At least one path additional to the slot isprovided alongwhich additional path or paths gases can also, flowbetween the interior of the drawing chamber and the interior of theannealing shaft.

Such apparatus affords the advantage that it enables sheet glass to bedrawn which is not impaired or which is less impaired by defects due tothe effects of turbulent thermally heterogeneous gas currents in theupper part of the drawing chamber. Various advantageous features whichcan be incorporated in apparatus according to the invention will now bereferred to. Many of these further features are for the purpose ofadopting process features which have already been described. Theadvantages of these further features of apparatus will be understoodfrom what has already been written about corresponding process features.

The invention includes apparatus in which there is at least oneadditional path via such gases can pass upwardly into the annealingshaft froma region of the drawing chamber'within the central thirdportion of the projected width of the ribbon path.

Preferably, apparatus according to the invention incorporates at leastone additional path via which gases can pass upwardly into theannealing'shaft from a region in the top portion of the drawing chamberand within the central third portionof the projected width of the ribbonpath.

In simple embodiments of apparatus according to the invention there isat least one additional path through the top of the drawing chamber.

Preferably, the apparatus includes at least one additional flow path viawhich gases descending opposite an outer third portion of the projectedwidth of the ribbon can flow from the annealing shaft into the drawingchamber.

In certain apparatus according to the invention there is at least oneadditional path via which gases can flow into the annealing shaft from aregion in the drawing chamber located within the central third portionof the projected width of the ribbon path, and there is at least oneadditional path via which gases can simultaneously flow into the drawingchamber from regions in the annealing shaft which are opposite the outerthird portion of the ribbon path.

It is possible to bring about the flow of gases via the additional flowpath or flow pathswithout employing special devices, e.g., propellers,for maintaining such flow. Thus according to certain embodiments ofapparatus according to the invention there is at least one additionalpath via which gases can flow between the drawing chamber and tbeannealing shaft due to natural convection currents. I

Preferably, apparatus according to the invention incorporates at leastone additional path on each side of the path or the ribbon.

The invention includes apparatus in which there is at least oneadditional flow path via which gases can descend from theinterior ofthe; annealing shaft into the drawing chamber, which path or paths is orare formed in such a way as to cause such descending gases to bedispersed at or near the top of the drawing chamber. In a simple form ofapparatus functioning in that way there is a plurality of additionalflow paths via which gases can descend from the interior of theannealing shaft into the drawing chamber and which are constituted byopenings defined by meshes of a screen; By way of-example there may beperforated plate screens, screens formed by woven filaments, or screensformed by spaced bars, such screens being located on opposite sides ofthe ribbon path at the top of'the drawing chamher and being spaced'apartso that the ribbon slot is delined by the inner edges of such screens.

The invention also includes apparatus in which there is at least oneadditional flow path via which gases can descend from the interior ofthe annealing shaft into the drawing chamber, which path or paths is orare formed in 'such a way as to di'spersesuch descending gases away fromthe path of the ribbon. in a simple form of apparatus functioning inthis way, there is a plurality of additional flow paths for descendinggases, such path or paths being defined by vanes which deflect Apparatusaccording to the invention may be of any one ofa variety of differentbasic designs; For example, the invention includes apparatus having amolten glass feed channel for holding a bath of molten glass of suchdepth that molten glass flows into the ribbon from the full depth ofsuch bath apparatus having a molten glass feed channel for holding abath of molten glass of such depth that the molten glass which flowsinto the ribbon is derived from the upper levels of such bath andapparatus having a molten glass feed channel along which molten glassfeeds to the-drawing zone while floating on a mass of material of higherspecific gravity.

The invention includes sheet glass when manufactured by a'proc'essaccording to the invention or in apparatus according to the invention ashereinbefore defined.

BRIEF DESCRIPTION OF THE DRAWINGS I DESCRIPTION OF THE PREFERREDEMBODIMENTS It is emphasized that the embodiments illustrated in thedrawings are entirely non-limitative. They' have been selected merely toillustrate a few ways of carrying out the invention. Moreover, while thedrawings illustrate the invention as applied to Pittsburgh-type glassdrawing processes and'machines, the invention is the descending gasesaway from the path of the ribbon.

flow paths, e.g., one or more screens or vanes, can be heated; Theheating of means defining a flow path for descending gases has theeffect of slowing down the descending gas currents and thus making themless liable to give rise to turbulent flow and unsettled thermalconditions adjacent the ribbon in the upper part of the drawing chamber.

In certain special forms of apparatus according to the invention thereis at least one additional path along which gases can flow into theannealing shaft from a region in the lower part of the drawing chamber.Thus, the invention includes apparatus in which there is at least onecooler located within the lower part of the drawing chamber, and inwhich there is at least one additional path which leads into theannealing shaft from a region of the drawing chamber in the vicinity ofa cooler. 1 Y

Preference is given to apparatus according to the insurmounting thedrawing chamber.

also applicable to the other types of glass drawing processes andmachines.

As the drawing machines shown in the drawings are entirely analagous asregards their basic structure, the same reference numerals-have beenused through the whole series of figures for identifying parts of thedifferent drawing machines which are strictly identical.

In themachine represented in FIG. l, a continuous glass ribbon is drawnupwardly from the surface of a supply of molten glass 2 which'is held ina kiln, the

structure of which kiln includes a terminal end wall 3 In aclassicalPittsburgh-type drawing machine there are so-called catch panswhich extend inwardly towards the path of the glass ribbon from the rearand front.

walls of the annealing-shaft, the inner boundaries of these catch pansbeing slightly spaced from one another so as to leave a slot for thepassage of the ribbon from the drawing chamber into the annealing shaft.The machine represented in FIG. 1 involves a modification of thisclassical construction in that the normal catch pans are dispensed with.At the bottom of the annealing shaft there are narrow inwardly extendinghorizontal flanges 13 and 14 which are well spaced from the path of theglass ribbon in order to leave room for the accommodation of a system ofvanes as will presently be described.

The glass ribbon is drawn upwardly by a series of drawing rollersrotatably mounted in the annealing shaft 12 on opposite sides of theglass ribbon path.

In the drawing chamber there are the customary principal coolers 16, 17which are located on opposite sides ofthe ribbon path, close to thesurface of the supply of molten glass 2.

ln the upper part of the drawing chamber there are secondary coolers l8,19, also located in opposite sides of the ribbon path. The principalcoolers l6, l7 and the secondary coolers 18, 19 are cooled by a coolingfluid, usually water, which is circulated through the coolers viaconduits (not shown).

In conventional glass drawing processes, using a classicalPittsburgh-type glass drawing machine, the strong natural draft forcesdue to the chimneyefi'ect of the annealing shaft, cause hot gas currentsto flow upwardly along the central region of the ribbon from theintensely hot drawing'zone, through the drawing chamber and into theannealing shaft, via the aforesaid ribbon slot whereas cooler currentsof gas flow back into the drawing chamber from the annealing shaft alongthe walls of the apparatus, mainly in the regions of the side margins ofthe ribbon path.

The descending cooler currents of gas mix with the hotter gases on thedrawing chamber, forming a thermally heterogeneous mixtureof gases whichcontacts the ribbon of glass in the top portion of the drawing chamber.The adverse environmental conditions in this region are also contributedto by the relatively high velocity of the hot gas currents ascendingthrough the top portion of the drawing chamber, towards the said ribbonslot.

Thus there is formed a complex system of currents as hereinbeforereferred to, which is thought to be at least in large part responsiblefor the aforesaid surface defects in the sheet glass.

The cooling action exerted by the secondary coolers on the environmentalgases in the upper part of the drawing chamber may accentuate theadverse effects of the complex system of gas currents by increasing thevelocity of certain of the downward currents. In any event, the actionof the secondary coolers tends to influence the environmental conditionsin' a way which gives rise to the occurrence of certain surface defectsin the drawn sheet glass.

ln the embodiment of the invention represented in FIG. 1, means isprovided .which modifies the nonnal pattern of currents in the upperpart of the drawing chamber in such a way as to reduce or avoid theturbu lence and the high'velocity of the currents.

The means which is responsible for this beneficial re-' sult includes asystem of vanes 20. In this case there are eight vanes disposed inspaced relation, four on each side of the ribbon path, and the vanes onopposite sides of the ribbon path are upwardly mutually convergent. Theresult of the provision of these vanes is that the slot via which theribbon 1 passes from the drawing chamber into the annealing shaft, isnot defined by catch pans as in a classical machine but by the innermostof the vanes 20 located on opposite sides of the ribbon path. Theimportant consequence of this arrangement 7 is that flow of gases fromthe drawing chamberinto the annealing shaft and vice versa can takeplace not only through the ribbon slot, and thus in close contact withthe ribbon .faces, but also through anumber of alternative paths, namelythe paths between neighboring vanes on each side of the ribbon path andbetween the outermost vanes and the flanges 13 and 14. As compared withthe classical process, the amount of high velocity gas which flowsthrough the ribbon slot in contact with the ribbon faces, in any givenperiod of time, is substantially reduced. This may be an importantreason why the described modification of the classical machine has theimportant beneficial effects which have'been referred to.

Another feature'of the illustrated embodiment 'of the invention, whichis thought to be of some importance, is the downward divergence of theopposed sets of vanes away from the ribbon path. Due to this downwarddivergence of the vanes away from the ribbon path, currents ofrelatively cold gas descending along the side walls of the annealingshaft are deflected away from the ribbon as they pass from this shaftinto the drawing chamber. Moreover the inclination of the vanes disturbsthe upward trajectories of the high speed hot currents of gas flowingupwardly towards the annealing shaft. I

The vanes 20 are pivotally mounted on horizontal axes so that theirinclination can be varied.

Due to the beneficial effects on the pattern of convection currents inthe upper part of the drawing chamber, it has been foundthat the drawingspeed of the glass ribbon can be increased above the maximum which wouldnormally be permissable for drawing glass of a predetermined surfacequality.

In the embodiment of the invention represented in FIG. 2, the ribbonslot, i.e,., the slot via which the ribbon passes from the drawingchamber into theannealing shaft, is defined not by the customary catchpans but by screens 22,23 of woven structure, which extend inwardly fromthe lateral flanges 13,14. As a result, gas

can flow from the drawing chamber into the annealing shaft and viceversa, not only via the ribbon slot, but also via numerous alternativepaths which are spaced away from the faces of the glass ribbon, suchalternative paths being constituted by the openings or meshes in thescreens 22 and 23. By virtue of the provision of these screens, there isa dispersion of the'ga'scurrents flowing into and from the annealingshaft and the amount of gas which flows in undisturbed high velocitystreams in contact with the faces of the glass ribbon at the location ofthe ribbon slot is substantially reduced. It has been found that theprovision of the screens influences the environmental conditions in sucha way that the surface quality of the drawn sheet glass is considerablyimproved.

Reference isnow made to the embodiment of the. invention represented inFIG. 3. ln this embodiment, the ribbon slot 24 is defined by catch paths25,26 provided at the bottom of the annealing shaft 12. On oppositesides of the ribbon path there are conduits 27, 28 which extend throughregions outside the drawing machine and which place the interior of thedrawing chamber 7 into communication with the interior of the annealingshaft 12. The conduits 27, 28 are of elongated cross section, the majoraxes of their cross sections being normal to the plane of the drawing.The conduits extend over approximately the central third of theprojected width of the ribbon path. However, the locations of at leastthe lower ends of the conduits relative to the projected width of theribbon can be adjusted. When the machine is in use, ascending currentsof hot gas can flow from the drawing chamber into the annealing shaft,not only via the ribbon slot 24 but also via the said conduits, whichthus constitute by-passes. At the rear side of the ribbon path, some ofthe ascending hot gas by-passes the slot 24 by flowing into the conduit27 through its inlet end portion 29, along this conduit 27, and into theannealing shaft 12 via the outlet end portion 30 of that conduit. At thefront side of the ribbon, some of the hot ascending gas enters the inletend portion 31 of the conduit 28, flows along this conduit and entersthe annealing shaft 12 via the outlet end portion 32 of that conduit.The velocity of flow of hot gases through the ribbon slot 24, in contactwith the faces of the ribbon, is therefore substantially reduced.

to reduce the high velocity of the gases through the ribbon slot.However, in other cases, it is preferred in this kind of embodiment toprovide means for promoting the flow of gases along the by-passconduits. Such means may for example take the form of small propelon thewalls and 'in the vicinity of the main coolers to be drawn from theenvironment of the ribbon into the boxes between the conduitsconstituting the main coolers 41 and 42, as indicated by the arrows inthe figure, the conduits being slightly spaced apart to permit this flowof gases between them. The gased drawn into the suction boxes 43 and 44are propelled along conduits 45 and 46 and discharge into the annealingshaft 12 at a level between the catch pans 39 and 40 and the first pairof drawing roller 15. In actual fact, the conduits 45 and 46 constitutethe injection tubes of two ejectors 47, 48. Each of theseejectors is ofknown type and in cludes a sleeve or diffuser which surrounds thedischarge end portion of the appertaining injection tube. When themachine is in use gas flows from the drawing chamber into the annealingshaft, not ony via the ribbon' slot 38, but also via the conduits 45 and46 which thus constitute by'passes. Due to the'fact that gases are drawninto the conduits 45, 46 from the interior of the drawing chamber anddischarge into the annealing shaft across thetop of the ribbon slot 38,the volume rate of flow of gases from the drawing chamber into theannealing shaft via the ribbon slot 38 is substantially reduced andthere is a concomitant reduction in the vollers mounted within theconduits. As an alternative,

combustion gas may be fed to discharge orifices located within theconduits and burns within the conduits so as toigenerate convectioncurrents therein.

In the embodiment of the invention represented in FIG. 4, the ribbonslot 33 is defined by catch pans 34, 35 but unlike conventional catchpans, these catch pans are formed with apertures 36, 37 which providealternative paths for the flow of gas from the drawing chambe'r into theannealing shaft and vice versa. There is a series ofapertures36,disposed in spaced relation along the catch pan 34 and a series ofapertures 37 disposed in spaced relation along the catch pan 35. Theascending currents of hot gas which do not actually pass through theribbon slot 33, will tend to pass through the apertures 36 and 37 whichare opposite the projected central part of the ribbon width, whereas thedescending colder currents of gas which descend mainly along the sidewalls of the annealing shaft will flow in part through the end portionsof the ribbon slot 33, i.e., the portions of this slot which aretraversed by the outer portions of the ribbon width, and in part throughthe apertures 36 and 37 which are opposite such outer portions of theribbon width so that such descending colder currents tend to remainlocalized in the vicinity of the side walls of the apparatus, and thustend not to contact the faces of the glass ribbon.

Reference is now made to FIG. 5. In this embodiment of the invention theribbon slot 38 is defined by catch pans 39 and 40.

In the lower part of the drawing chamber there are principal coolers 41,42 comprising series of conduits through which cooling fluid is passed,and at the sides of these coolers which are remote from the ribbon paththere are suction boxes 43, 44 housing propellers (not shown) whichcause cold gas currents which originate ume rate of flow of relativelycold gases from the annealing shaft into the drawing chamber. As aresult, the

process, the invention can also be embodied in other processes andmachines, eg in processesand machines in which the glass ribbon, afterbeing drawn upwardly from the supply of molten glass, is bent around abending roll in the drawing chamber and then passes along asubstantially horizontal annealing shaft. In such processes and machinesthe glass ribbon also travels through a slot between the drawing chamberand the annealing shaft. It will be understood that the abovedescription of the present invention is susceptible to variousmodifications, changes and adaptations, and the same are intended to becomprehended within the meaning and range of equivalents of the appendedclaims.

We claim: 1. Apparatus for use in manufacturing sheet glass, comprising,in combination:

a drawing chamber; I a contiguous annealing shaft which communicateswith such drawing chamber; means defining a slot through which suchcommunication takes place; means for drawing a continuous ribbon ofglass from a supply of molten glass at a drawing'zone so that the ribbonpasses through such drawing chamber and into the annealing shaft throughsaid slot and convection currents of gases also flow through such slotfrom the drawing chamber into the annealing shaft and vice versa; and

means defining at least one gas flow path said means interior of thedrawing chamber and the interior of the annealing shaft, said meansbeing arranged between said chamber and said shaft to direct gases alongsaid path by natural convection currents only.

2. Apparatus as defined in claim 1 wherein in at least one suchadditional path gases can pass upwardly into the annealing shaft from aregion of the drawing chamber within the central third portion of theprojected width of the ribbon path.

3. Apparatus as defined in claim 2 wherein in at least one suchadditional path gases can pass upwardly into the annealing shaft from aregion in the top portion of the drawing chamber and within thecentralthird portion of the projected width of the ribbon path.

4. Apparatus as defined in claim 1 wherein at least one such additionalpath is through the top of the drawing chamber.

5. Apparatus as defined in claim 1 wherein in at least one suchadditional flow path gases descending opposite an outer third portion ofthe projected width of the ribbon can flow from the annealing shaft intothe draw ing chamber.

6. Apparatus as defined in claim 1 wherein in at least one suchadditional path gases can flow into the annealing shaft from a region inthe drawing chamber located with the central third portion of theprojected width of the ribbon path and there is at least one suchadditional path via which gases can simultaneously flow into the drawingchamber from regions in the annealing shaft which are opposite the outerthird portions of the ribbon path.

7. Apparatus as defined in claim 1 wherein there is at least one suchadditional flow path on each side of the path of the ribbon.

8. Apparatus as defined in claim 1 wherein there is at least one suchadditional flow path via which gases can descend from the interior ofthe annealing shaft into the drawing chamber, which path is arranged sothat descending gases are dispersed at or near the top of the drawingchamber.

9. Apparatus as defined in claim 1 wherein said gas 14 flow pathdefining means is located in said slot defining means. i

10. Apparatus as defined in claim 9 wherein there is a plurality of suchadditional flow paths which are constituted by the openings of a screen.

11. Apparatus as defined in claim 1 wherein there is at least one suchadditional flow path via which gases can descend from the interior ofthe annealing shaft into the drawing chamber, which path is arranged sothat descending gases are dispersed away from the path of the ribbon. I

12. Apparatus as defined in claim 9 wherein there is a plurality of suchadditional flow paths which are defined by vanes.

13. Apparatus as defined in claim 1 wherein there is at least one suchadditional path along which gases can flow into the annealing shaft froma region in the lower part of the drawing chamber. 7

14. Apparatus as defined in claim 13 comprising at least one coolerlocated within the lower part of the drawing chamber and wherein atleast one such additional path leads into the annealing shaft from aregion of the drawing chamber in the vicinity of said cooler.

molten glass feed channel for holding a bath of molten glass of suchdepth that the molten glass which flows into the ribbon is derived fromthe upper level of such bath.

18. Apparatus as defined in claim 1 comprising a molten glass feedchannel along whichmolten glass feeds to said drawing zone whilefloating on a mass of material of higher specific gravity.

.line 6, change "gased" to gases-.

% McCOY M. GIBSON JR.

UNITED STATES PATENT oFFicE CERTIFICATE OF CORRECTION Dated April 2nd,1974 Patent No. 3 3

Inventor(s) Michael Lambert, Hubert Neuzy, Claude Brichard It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below: In the headingof the patent, line 2, change "Michael" to Michel. Column 1, line 39change "locations" to --location---; line 55, change "ribbons" to-ribbo'n--. Column 3, line 12, change "he" to the--; line 15 change"shaft"to -draft. Column 4 lines 11 and 12, change -I "locations" to--'-location-; line 58, correct spelling of "caused" Column 6 line 44,change "such" to -which. Column 11, line 17, change "shaft" to draft'--.Column 12,

Column 13, line 27, change "with" to -within- Signed and sealed this 1stday of October; 1974.

(SEAL) Attest:

c. MARSHALL DANN attesting Officer Commissioner of Patents USCOMM-DCOOEVIG-PSQ u s ccvzmmnn Pmm'wc. ornc: 1 mm 0-166-334.

)RM PO-TOSO (10-69)

1. Apparatus for use in manufacturing sheet glass, comprising, incombination: a drawing chamber; a contiguous annealing shaft whichcommunicates with such drawing chamber; means defining a slot throughwhich such communication takes place; means for drawing a continuousribbon of glass from a supply of molten glass at a drawing zone so thatthe ribbon passes through such drawing chamber and into the annealingshaft through said slot and convection currents of gases also flowthrough such slot from the drawing chamber into the annealing shaft andvice versa; and means defining at least one gas flow path said meansbeing of sufficient cross sectional area to reduce the volume rate offlow of gas between the drawing chamber and annealing shaft via saidslot in addition to the gas flow path provided by said slot fordirecting gases to flow along such path between the interior of thedrawing chamber and the interior of the annealing shaft, said meansbeing arranged between said chamber and said shaft to direct gases alongsaid path by natural convection currents only.
 2. Apparatus as definedin claim 1 wherein in at least one such additional path gases can passupwardly into the annealing shaft from a region of the drawing chamberwithin the central third portion of the projected width of the ribbonpath.
 3. Apparatus as defined in claim 2 wherein in at least one suchadditional path gases can pass upwardly into the annealing shaft from aregion in the top portion of the drawing chamber and within the centralthird portion of the projected width of the ribbon path.
 4. Apparatus asdefined in claim 1 wherein at least one such additional path is throughthe top of the drawing chamber.
 5. Apparatus as defined in claim 1wherein in at least one such additional flow path gases descendingopposite an outer third portion of the projected width of the ribbon canflow from the annealing shaft into the drawing chamber.
 6. Apparatus asdefined in claim 1 wherein in at least one such additional path gasescan flow into the annealing shaft from a region in the drawing chamberlocated with the central third portion of the projected width of theribbon path and there is at least one such additional path via whichgases can simultaneously flow into the drawing chamber from regions inthe annealing shaft which are opposite the outer third portions of theribbon path.
 7. Apparatus as defined in claim 1 wherein there is atleast one such additional flow path on each side of the path of theribbon.
 8. Apparatus as defined in claim 1 wherein there is at least onesuch additional flow path via which gases can descend from the interiorof the annealing shaft into the drawing chamber, which path is arrangedso that descending gases are dispersed at or near the top of the drawingchamber.
 9. Apparatus as defined in claim 1 wherein said gas flow pathdefiNing means is located in said slot defining means.
 10. Apparatus asdefined in claim 9 wherein there is a plurality of such additional flowpaths which are constituted by the openings of a screen.
 11. Apparatusas defined in claim 1 wherein there is at least one such additional flowpath via which gases can descend from the interior of the annealingshaft into the drawing chamber, which path is arranged so thatdescending gases are dispersed away from the path of the ribbon. 12.Apparatus as defined in claim 9 wherein there is a plurality of suchadditional flow paths which are defined by vanes.
 13. Apparatus asdefined in claim 1 wherein there is at least one such additional pathalong which gases can flow into the annealing shaft from a region in thelower part of the drawing chamber.
 14. Apparatus as defined in claim 13comprising at least one cooler located within the lower part of thedrawing chamber and wherein at least one such additional path leads intothe annealing shaft from a region of the drawing chamber in the vicinityof said cooler.
 15. Apparatus as defined in claim 1 wherein theannealing shaft is a vertical shaft surmounting the drawing chamber. 16.Apparatus as defined in claim 1 comprising a molten glass feed channelfor holding a bath of molten glass of such depth that molten glass flowsinto the ribbon from the full depth of such bath.
 17. Apparatus asdefined in claim 1 comprising a molten glass feed channel for holding abath of molten glass of such depth that the molten glass which flowsinto the ribbon is derived from the upper level of such bath. 18.Apparatus as defined in claim 1 comprising a molten glass feed channelalong which molten glass feeds to said drawing zone while floating on amass of material of higher specific gravity.